The invention is based on a device for adjusting the spring characteristic of a helical spring as generally defined hereinafter.
In a known apparatus of this type for an rpm governor of a fuel injection pump, the retaining member is embodied by a housing having an internal bore, in which the adjusting tang is mounted concentrically on a governor rod and is rotatably retained with a slide collar that protrudes beyond the circumference. The adjusting tang protrudes beyond the housing and there has a hexagonal head intended for engagement with any suitable tool or wrench. The retaining member is embodied as an annular disk which covers the annular opening remaining between the adjusting tang and the housing and is firmly joined to the housing on its annular face oriented toward the interior of the housing and this annular disk has a spur gear. The spur gear is engaged by a similar face gear disposed on the slide collar. The adjusting tang has a helical outer groove, in which a portion of the windings of the helical spring is guided. On the end remote from the adjusting tang, the helical spring is supported on a supporting member that is firmly joined to the governor rod and thereby presses the two spur gears into one another. To vary the spring characteristic, the hexagonal head of the adjusting tang msut be rotated, in the course of which the spur gears act as a sort of slip coupling, and depending on the direction of rotation the adjusting tang is screwed increasingly farther out of or into the helical spring. In either case, the number of windings available in the free spring length of the helical spring is varied, and hence the spring stiffness is changed. Additionally, in the first case the spring bias is increased, while in the second case it is decreased. Thus when adjusting the spring characteristic, varying the pitch of the spring steepness is inseparably associated with varying or prestressing the spring.
In a further known apparatus of the above type for adjusting the spring stiffness of an rpm governor spring in a fuel injection pump, the retaining member is embodied by a strut-like housing part which has a threaded through bore. The adjusting tang, embodied as a screw, can be screwed with its external thread into the internal thread of the threaded through bore. The arresting member is embodied as a nut mounted on the adjusting tang; by being rotated, the nut can be pressed on the helical thread of the adjusting tang on the housing, thus securing the instantaneus rotational position of the adjusting tang. The adjusting tang protrudes into the interior of the helical spring and has two radially offstanding pins, preferably on the end oriented toward the helical spring, which pin protrude between the windings of the helical spring. To adjust the spring characteristic, the nut must be loosened and the adjusting tang rotated appropriately in the housing thread. With the use of the two radial pins, the adjusting tang is thereby screwed to a variable extent into the helical spring. Since the radial pins act as one support of the helical spring, the free spring length of the helical spring is thereby varied. In this known apparatus, the spring biasing is not adjustable.